O’Connor, Ken. How to Grade For Learning: Linking Grades to Standards, 2002. Reeves, Doug. “The Case Against the Zero.” Phi Delta Kappan; Dec 2004, 324-325. Other researchers: Rick Wormelli, Rick Stiggins, Robert Marzano, Tom Guskey, Doug Reeves, and Jay McTighe.
“…the common use of the zero today is based… on a 100-point scale. This defies logic and mathematical accuracy. On a 100-point scale, the interval between numerical and letter grades is typically 10 points, with the break point at 90, 80, 70, and so on. But when the grade of 0 is applied to a 100-point scale, the interval between the D and [E] is not 10 points but  points.” – Douglas Reeves
“…we should teach and grade in such a way that engenders hope… [and] accuracy. [Eliminating the 6 levels of failure] will mitigate an extraordinary negative impact.” – Rick Wormeli “The inclusion of [a] 0 in the grade [can lead] to a serious miscommunication of… achievement.” – Ken O’Connor